Point-to-point radio systems using microwaves, millimeter waves or the like are known (see, for example, Patent Literature 1 and 2). In a point-to-point radio system, two communication apparatuses perform digital communication via a point-to-point radio link. To be more specific, each of the communication apparatuses is equipped with a directional antenna to communicate with a counterpart apparatus by means of a point-to-point radio technology and forms a directional beam toward the counterpart apparatus. The point-to-point radio link is thus established between the two communication apparatuses. In this specification, each of the two communication apparatuses constituting the point-to-point radio system, i.e., a communication apparatus that communicates with a counterpart apparatus using the point-to-point radio technology is referred to as a point-to-point radio apparatus.
Point-to-point radio systems are used in, for example, a mobile backhaul. The mobile backhaul includes both a network that connects a base station in a cellular communication system to a site where a higher network node is installed and a network that connects between base stations. Each base station is, for example, a Base Transceiver Station (BTS), a NodeB, or an eNodeB. The higher network node is, for example, a Base Station Controller (BSC), a Radio Network Controller (RNC), a Serving General Packet Radio Service Support Node (SGSN), a Serving Gateway (S-GW), or a Mobility Management Entity (MME). Advantages of point-to-point radio systems over wired connections with optical fibers are, for example, easy network construction, high economic efficiency, and fewer restrictions on installation locations of base stations.
Point-to-point radio systems commonly support simultaneous bidirectional communication (full-duplex communication). Accordingly, a point-to-point radio link includes a bidirectional pair of radio links. In this specification, one of the bidirectional pair of radio links is referred to as a forward link, while the other one is referred to as a reverse link. Further, when a point-to-point radio system is used in a mobile backhaul, a radio link in a direction from a higher network node toward a base station is defined to as a forward link, while a radio link in a direction from a base station to a higher network node is defined as a reverse link.
In one example, a point-to-point radio system uses Frequency Division Duplexing (FDD) or Time Division Duplex (TDD) to perform simultaneous bidirectional communication (full-duplex communication). In the case of FDD, two different radio channels are used for the bidirectional pair of radio links. In the case of TDD, one radio channel is used for the pair of radio links in a time-sharing manner. Each radio channel may be referred to as a radio frequency carrier.